1. Field of the Invention
This invention relates to an improved grouting composition for an anchor element, the composition comprising (1) pressure sensitive liquid containing microcapsule particles, and (2) non-pressure sensitive hydraulic cement powder particles. The grouting composition is desirably in the form of a cartridge comprising an elongated tubular casing.
2. Description of the Prior Art
Considerable effort has gone into developing means for anchoring roof bolts as part of an effort to prevent roof collapses in mines. Obviously, there are many other applications that require grouting of an anchor element in a hole of a support structure.
The common commercial anchor element cartridge in use today comprises reactive components of a resin with the components in separate compartments of an elongated tubular casing which are brought into contact with one another upon injecting a bolt, thereby forming a hardened resin which anchors the bolt into the base.
Since ventilation is often a serious problem in mines, the fumes that are given off by the reaction of the reactive components of the resin can cause serious health hazards to those people who have to work in the mines.
Therefore, efforts have been made to produce anchor element cartridges which would provide effective fastening for the anchor element in a hole of a support structure and not give off the harmful fumes. One such successful solution to this problem is disclosed in U.S. Pat. No. 4,096,944, incorporated herein by reference, wherein an anchor element cartridge is described comprising water-containing microcapsules which are pressure sensitive combined with non-pressure sensitive hydraulic cement powder. When an anchor element is injected into the elongated cartridge which is in an elongated bore hole in the roof of a mine, the pressure from the anchor element causes a reaction to take place between the hydraulic cement powder and the water which is released from the pressure sensitive microcapsules. These cartridges do an effective job of anchoring without the harmful fume problem of the resin cartridges.
However, one of the problems with the hydraulic cement cartridges is that the cost of manufacture using the conventional manufacturing equipment used for the resin cartridges produce a cartridge which is as expensive as the conventional resin cartridge. Efforts to solve this problem initially were not successful because in the attempt to mix and package the pressure sensitive microcapsules and the hydraulic cement powders the microcapsules would break, thereby causing pre-mature hardening of the cartridges.
A solution to this problem is proposed in co-pending U.S. patent application Ser. No. 337,657 filed on even date entitled, "Anchor for Manufacturing Anchor Element Cartridges" by Donald L. Douty. This co-pending application is incorporated herein by reference. The apparatus described therein provides a much higher production rate. However, difficulty was experienced in achieving the desired level of production. Also, difficulty as experienced in maintaining a uniform ratio of liquid-containing capsules to inorganic cement powder, particularly at the high production rates.